This invention relates to disc storage apparatus employing patterned storage media, and particularly to patterned media for use in disc drives having aerodynamic transducers with minimal fly heights.
Patterned media of magnetic disc drives employ magnetic recording discs having a predetermined pattern of surface irregularities in the form of depressions, such as pits or grooves, and/or raised areas, such as bumps and lands, that define a servo pattern within servo sectors. The user data are magnetically recorded on the medium and read from the medium through magnetic recovery techniques. The servo pattern is permanently formed in the medium as surface irregularities. The pattern of surface irregularities is read from the medium using thermal or optical techniques.
Patterned disc media are commonly employed in magnetic disc drives having aerodynamically flying transducers comprising a slider and a read/write head. The slider includes an air bearing surface that xe2x80x9cfliesxe2x80x9d the head adjacent the rotating disc. In one form, magnetoresistive read heads transfer heat generated by the sense current to the medium to dissipate within the medium. When confronting the surface irregularities of the servo pattern, changes in distance between the flying transducer and each depression or raised area changes the heat transfer characteristics between the transducer and the medium, thereby altering the resistance of the magnetoresistive head. Consequently, the resistance of the head changes with the servo pattern manifest in the surface irregularities, and the servo pattern can be electronically recovered from the voltage across the head. Patterned media are also used in environments where the user data are recorded and recovered magnetically while the servo data are recorded and recovered optically, similar to techniques used in optical disc drives.
One problem of patterned discs is that the pattern of surface irregularities causes fly height perturbations of the flying head, creating a modulating fly height of the head over the disc. Typically, the depth of the depressions or height of the raised areas forming the servo patterns on a patterned medium is about 10 to 25 nanometers. The surface irregularities are usually so tightly packed and numerous that the slider passing over the servo sector aerodynamically xe2x80x9cseesxe2x80x9d one large depression or one large raised area having a length along the track equal to the length of the servo pattern, such as about 20 to 80 microns and an apparent depth or height about one-half the depth or height of the pits or bumps. Consequently, the slider aerodynamically sees a xe2x80x9cvalleyxe2x80x9d or xe2x80x9chillxe2x80x9d in the servo sector that is 5 to 12.5 nanometers deep or high, 20 to 80 microns long, and as wide as the slider. As the slider passes over this xe2x80x9cvalleyxe2x80x9d or xe2x80x9chillxe2x80x9d formed by the servo sector, fly height perturbations as large as 5 to 10 nanometers may occur.
As the trend toward increasing disc track density continues, there is a corresponding need to minimize the fly height of the head. More particularly, nominal fly heights of 10 nanometers or less is required for some high track density drives. Since it is normally necessary to maintain fly height perturbations at no more than 10% of the nominal fly height, perturbations of less than xc2x11 nanometer are required for high track density drives. The present invention provides a solution to this and other problems, and offers other advantages over the prior art.
In one embodiment of the invention, a patterned magnetic storage medium has a plurality of data sectors separated by respective servo sectors and a plurality of parallel tracks extending through the servo sectors and data sectors. Each servo sector has a pattern of first surface irregularities, such as pits or lands, representing servo data. A second surface irregularity, such as a groove or ridge, in each data sector separates adjacent tracks, with each first and second surface irregularity having an elevation, such as a depth or height, different from a nominal surface of the medium. Non-uniform means are so disposed and arranged that a slider adjacent the medium is modeled with minimum fly height perturbations when the slider is moved at a selected velocity along the tracks.
In preferred forms, the non-uniform means includes third surface irregularities, such as lands or pits, in the second surface irregularities that are pseudo-randomly spaced along each second surface irregularity to form segments of pseudo-random length and are pseudo-randomly positioned across the data sector.
In another embodiment, the storage medium is arranged to move at a predetermined velocity relative to a slider to cause the slider to fly along a track over the data sectors and servo sectors. The servo sectors have a length along each track that defines a null frequency that matches a pitch frequency of modulation of the slider due to the first surface irregularities of the servo sectors.
In another embodiment, a patterned storage medium is fabricated by forming surface irregularities, such as pits or lands, to an elevation, such as a depth or height, different from a nominal surface of the medium to define servo sectors separating data sectors on the medium. A plurality of tracks are defined through data sectors and servo sectors. A plurality of second surface irregularities, such as grooves or ridges, are formed parallel to each track through the data sectors, and a plurality of third surface irregularities, such as lands or pits, are formed in the grooves or ridges to segment the grooves or ridges. The third surface irregularities are arranged so that when the medium is moved at a selected velocity along the tracks, a slider adjacent the medium is modeled with minimum fly height perturbations when the slider is moved at a selected velocity along the tracks.
In another embodiment, the length of each servo sector along each track is defined to minimize modulation of an aerodynamic slider arranged to fly adjacent the medium.
Other features and benefits that characterize the present invention will be apparent upon reading the following detailed description and review of the associated drawings.